Hyperef problema pdf

Documentazione: texdoc pdftex, pagina 18:

\pdfminorversion (integer)

This primitive sets the pdf version of the generated file and the latest allowed pdf version of included pdfs. E. g., \pdfminorversion=3 tells pdfTEX to set the pdf version to 1.3 and allows only included pdf files with versions numbers up to 1.3. The default for \pdfminorversion is 5, producing files with pdf version 1.5. If specified, this primitive must appear before any data is to be written to the generated pdf file, so you should put it at the very start of your files. The command has been introduced in pdfTEX 1.30.0 as a shortened synonym of \pdfoptionpdfminorversion command, that is obsolete by now.
Distributions alter the default value here; for example, TEX Live 2010 sets \pdfminorversion=5 when its formats are built, so object compression can be enabled (described below).

Nel preambolo, quindi devi impostare [tt]\pdfminorversio=4[/tt]